Women in some manufacturing occupations have double the normal risk of developing breast cancer, according to a landmark Canadian study.

The results, published Monday and among the first to extensively look at a number of occupations, could have widespread implications in forcing governments to review and adopt stricter regulations to safeguard the health of women in these blue-collar industries.

“Most public-health initiatives have overlooked the seemingly invisible cohort of farm and blue-collar women workers, who are providing us with consumer goods,” said lead author James Brophy, an adjunct professor at the University of Windsor. “We think that the findings from this study have important implications for women … and point to the need to rethink our regulatory protections and compensation systems.”

The team of researchers from Canada, the United States and Europe believe that women in these workplaces are exposed to mammary carcinogens and other chemicals that place them at increased risk of breast cancer. The study involved more than 1,000 women with breast cancer and another 1,147 women without the disease, a control group, in the Windsor and surrounding Essex and Kent County, areas where there is extensive manufacturing and agriculture. Participants provided detailed occupational histories as well as information on reproductive risk factors, including pregnancies, history of breastfeeding, alcohol use and smoking.

The study, published in the journal Environmental Health, found:

Women in food canning production were twice as likely to develop breast cancer, with the authors saying exposure to vapours from bisphenol A (BPA) can linings and to pesticides from the food being heated, processed and packaged may be playing a role; Women in the automotive plastics industry may be exposed to a mixture of solvents, glues and other chemicals, and were twice as likely to develop breast cancer; Females working in casinos and in bars are also twice as likely to develop breast cancer, which may be linked to second-hand smoke exposure and night work, which has been found to disrupt the endocrine system; Women in the metalworking industry may be exposed to fumes, solvents, smoke and an array of toxic chemicals, and have a 73-per-cent increased risk of breast cancer compared to women in the general population; Farm workers may be exposed to chemicals such as pesticides, fungicides, fertilizers, other agricultural chemicals and diesel exhaust from farm equipment, and have a 36-per-cent increased risk of breast cancer.

Dr. Brophy said he is concerned that Canadian authorities are paying little attention to such a serious issue. Co-author Margaret Keith, also an adjunct professor at the University of Windsor, said much effort has gone into making sure baby bottles are free of BPA, but officials have not considered the women and men exposed to the hormone-mimicking chemical.

“We don’t really know what the exposure levels are inside these plants,” Dr. Keith said. “I think the regulations haven’t taken into account what we now know scientifically.”

A spokeswoman for Health Canada said the government agency is committed to protecting those in the workplace. Health Canada provides about $600,000 annually to a project aimed at identifying the prevalence of workplace carcinogens, the spokeswoman said in an e-mail.

The Ontario Ministry of Labour also said it is actively addressing the issue. “We make decisions on the latest science and we welcome any report that will bring a better understanding of occupational exposures to ensure that workers are protected from unsafe exposure levels,” a spokesman said.

For breast-cancer patients, like Carol Bristow, change cannot come soon enough. A machine operator at a plastics company, she breathed in solvents, glues and other chemicals – exposure, Ms. Bristow feels, that led to her breast-cancer diagnosis two decades ago.

She lost her right breast and ended up having a hysterectomy in order to reduce the hormones that were fuelling the cancer. Yet, she returned to her job at an auto-parts manufacturing company in Windsor, Ont., despite opposition from those who cared for her during her illness.

“You lose so much money when you’re sick, and go you back to work because you get benefits, and then you get sick again,” said Ms. Bristow, 54. “It’s a scary situation.”

Paul Demers, director of the Occupational Cancer Research Centre, urged caution in drawing a link between chemicals in these industries and the risk in developing breast cancer. Dr. Demers has received a $1-million grant from the Canadian Cancer Society to study the impact of workplace exposure to 44 known or suspected carcinogens and their links to different types of cancer. He said Dr. Brophy’s findings are important because this is an understudied area.

“We need more evidence in human studies … that these chemicals are cancer-causing,” Dr. Demers said.